1. Field of the Invention
The invention is generally related to an isolation technique which prevents vibrations from the X-Y stages, substrate handling systems, vacuum systems, and ground frame of a lithography tool from adversely impacting on the performance of the exposure module.
2. Description of the Prior Art
Lithography tools typically have the exposure system (e.g., electron column for an E-beam lithography system), X-Y stages for masks and/or substrates, the substrate and mask handling systems, and the vacuum systems all mounted on a common isolation plate. The isolation plate is supported in such a way as to prevent floor vibration from reaching critical parts of the lithography tool. This prior art arrangement does not prevent vibrations generated by the X-Y stages and stage drivers, the substrate and mask handling systems, and the vacuum systems from being transmitted to the exposure system and adversely impacting on throughput and performance. In order to properly expose a substrate or film, such as a photoresist material or the like, all subsystems must be idle or mechanically quiet, otherwise, the tool vibrations will cause a degradation in pattern placement accuracy.
Early generation E-beam tools are typically operated at very slow rates of speed. Vibration problems have traditionally been handled by allowing a sufficient time period for the vibrations in the subsystems to dampen down to an acceptable level before proceeding with further exposure processes. However, with the later generation scanning and reduction-projection E-beam lithography systems, throughput is an important concern. It would be advantageous to provide a lithography tool with a vibration isolation scheme that provides complete isolation of the exposure system, and allows other operations such as high speed stage motions and substrate handling operations to be performed simultaneously with the lithography.
U.S. Pat. No. 4,352,643 to Iijima discloses isolation of vibrations produced by a vacuum pump from being transmitted to a vacuum apparatus, such as an E-Beam exposure apparatus, electron microscope, or the like. In Iijima, the pump is suspended from the main chamber using a bellows. The pump rides on a guide rail and utilizes the bellows as the fulcrum of a pendulum. Thus, in operation, reciprocating movement of pistons in the pump cause the pump to ride on the guide rail in a pendulum fashion, and the bellows prevents the vibrations from being transmitted to the main portion of the apparatus. The Iijima reference fails to recognize that a majority of vibrations in a E-Beam lithography apparatus are caused by movement of the masks and wafers, and movement of the stages, and Iijima makes no provisions to dampen these vibrations. Rather, as with other prior art systems discussed above, Iijima relies only on vibration insulators positioned on a common plane with the remaining subsystems. As explained above, these vibration insulators will only isolate the tool from floor vibrations.
U.S. Pat. No. 4,952,858 to Galburt discloses a microlithographic apparatus which can be used for imaging and/or inspection wherein the motor element is decoupled from the stage using a magnetic coupling arrangement wherein the monolithic stage is floating in space above the sub-stage. Galbourt mounts most components on a common stage which are isolated from the floor using spring isolators.
U.S. Pat. No. 5,308,036 to Olson et al. discloses a stand for a microscope wherein vertical vibrations are prevented from being transmitted from one leg to another using damping materials at the base of each leg.